Endoprosthetic elbow joint devices

ABSTRACT

An endoprosthetic elbow joint device of hingeless form comprises humeral and ulnar components which are each of trough form. The humeral component outer surface is of circular cylindrical form over at least part of its length and is secured to the humerus at its inner surface, while the ulnar component has a complementary circular cylindrical inner surface for mutually articulatory bearing engagement with the humeral component and is secured to the ulna at its outer surface. In a modification the humeral component has a convex, part-annular, part-spherically shaped extension to its outer surface, which extension articulates with a complementary concave surface of an additional component for securement to the radius.

United States Patent [191 Swanson et al.

[ ENDOPROSTHETIC ELBOW JOINT DEVICES [75] Inventors: Sydney Alan VaseySwanson,

Carshalton; Brian Arnold Roper, London, both of England [73] Assignee:National Research Development Corporation, London, England [22] Filed:Nov. 30, 1973 [21] Appl. No.: 420,578

[30] Foreign Application Priority Data Nov. 30, 1972 United Kingdom55350/72 [52] US. Cl. 3/191; 128/92 C [51] Int. Cl. A61F 1/24 [58] Fieldof Search 3/1, 1.9-1.912; 128/92 C, 92 CA, 92 R [56] References CitedUNITED STATES PATENTS 3,506,982 4/1970 Steffee 128/92 C X 3,521,3027/1970 Miiller 3/1 Nov. 18, 1975 Stevens 128/92 C Averill et a1. 3/1

[57] ABSTRACT An endoprosthetic elbow joint device of hingeless formcomprises humeral and ulnar components which are each of trough form.The humeral component outer surface is of circular cylindrical form overat least part of its length and is secured to the humerus at its innersurface, while the ulnar component has a complementary circularcylindrical inner surface for mutually articulatory bearing engagementwith the humeral component and is secured to the ulna at its outersurface. In a modification the humeral component has a convex,part-annular, part-spherically shaped extension to its outer surface,which extension articulates with, a complementary concave surface of anadditional component for securement to the radius.

9 Claims, 9 Drawing Figures US Patent .Nov. 18, 1975 3,919,725

1 ENDOPROSTI-IETIC ELBOW JOINT DEVICES This invention concernsprosthetic devices and relates particularly to endoprosthetic elbowjoint devices.

The forms of the latter devices in current usage normally involve adirectly-linked mechanical hinge of allmetal construction which issecured to the humerus and ulna by way of intramedullary stems. Whilesuch hinged devices have proved satisfactory in the shorter term, it isnow thought that they are subject to disadvantage in the longer term.More specifically, there is a tendency for the securement of the deviceto be weakened by transmission. of stresses through the device itself.There is, in any case, disadvantage in the relatively large removal ofbone and deep medullary penetration which is required for such hingeddevices.

An object of the present invention is to reduce these disadvantages and,to this end, provides an endoprosthetic elbow joint device, which, in amore general aspect, comprises: a humeral component in the form of a caphaving a generally U-shaped channel cross-section relative to alongitudinal axis therethrough, with an outer bearing surface ofcircular arcuatecross-seCtion centered on said axis, and an innerfixation surface encompassing said axis; and an ulnar component in theform of a socket hving an inner bearing surface of substantiallycomplementary shaping to at least a longitudinal position of said outerbearing surface to receive the same in mutually articulatory engagement,and an outer fixation surface, said inner and outer fixation surfacesbeing adapted for respective securement to the humerus and ulna.

The proposed device can take a first form which, in common with theconventional hinged form of device, involves excision of the distal headof the radius. In this first form the humeral component bearingsurfaceis preferably substantially circular cylindrical.

In a second form of the proposed device provision is made forreplacement of the radial articulation in the elbow joint function byaugmenting the humeral component and by the addition of a radialcomponent. In this case the humeral component is basically as definedabove with'a first portion of said outer bearing surface beingcomplementary with said ulnar component bearing surface, and a secondportion of said outer bearing surface being of convex, substantiallypart-spherical shaping, located adjacent one end of said first portion,centred on said axis, and having greater radius than said first portion.This second portion engages a radial component having a complementaryconcave bearing surface and a fixation surface.

Whatever the form of the proposed device, it is presently preferred thatthe humeral component be thinwalled relative to the ulnar component, andthat these components be made respectively of metal and plasticsmaterial. The radial component is also preferably of plastics materialin these circumstances.

Regarding the fixation surfaces of the components: these will normallybe intended to facilitate securement to the relevant bones with use ofacrylic cement or equivalent gap-filling medium, but without use of longintramedullary stems. For this purpose the fixation surfaces compriserelieved formations, such as grooves,

ribs or studs, which are preferably of shallow depth relative to thedimensions of the respective bearing surfaces, although such formationsmay in some circumstances be replaced or augmented by stems havinglengths not significantly greater than said dimensions.

, side views,

FIGS. 3, 4 and 5 illustrate the associated ulnar component of thisembodiment in respective end, side, and plan views,

FIG. 6 diagrammatically illustrates in a sectional view the positioningof the first embodiment relative to the humerus and ulna,

FIGS. 7 and 8 illustrate the humeral component of a second embodiment ofthe invention in respective end and side views, and

FIG. 9 illustrates the associated radial component of this secondembodiment in side view.

The humeral component of FIGS. 1 and 2 is a cap for the lower end of thehumerus, the cap'being denoted at 1 in the form of a cylindricalopen-ended through, having an outer bearing surface 2 of major segmentalcircular arcuate cross-sectional shape centred on'a longitudinal axis 3of the trough, and an inner fixation surface 4. encompassing the axis 3.The inner surface 4 has, as seen in FIG. 1, a cross-sectional shapingformed by a parallel-sided slot terminating in a semi-circular basecentred on the axis 3, this slot being in symmetrical relation with theouter bearing surface 2. The inner surface 4 does not have, a relievedformation, but such a formation may be appropriate by the provision ofslots or in equivalent manner.

The associated ulnar component of FIGS. '3 to 5 is a socket for theupper end of the ulna, the socket being denoted at 6-in the general formof an open-ended through having an inner bearing surface 7 ofminor-segmental circular arcuate cross-sectional shape and like radiusas the outer bearing'surface 2 of the humeral component to receive thesame in mutual articulatory bearing engagement. The longitudinal endportions of the side walls of the socket are smoothly downwardly taperedwith convex circular quadrant profiles 8 which are of equal radius inthe present instance, but may differ in other embodiments. The remainingouter surface 9 of the socket is of generally tapered orfrusto-pyramidal form converging remotely from the inner bearing surface7. Also, the outer surface 9 has a relieved formation which in thisinstance is provided by at least one V-shaped slot 10 extending acrossthe underneath of the trough as shown in FIG. 4.

In a modified form of this ulna component, the relieved formation isaugmented by the provision of a short stub 12 as shown in broken outlinein FIGS. 3 and 5.

The components of the embodiment just described are made of materialsaccording to the above-indicated preference, with the humeral componentbeing made of a metal such as a chrome-cobalt alloy or stainless steel,and the ulnar component being made of a plastics material such as highdensity polyethylene.

The positioning of the components relative to the associated bones isdiagrammatically illustrated by FIG. 6. The capitulum 21 of the humerus22 is retained, while the trochlea 23 of the humerus is cut down to fitthe channel cavity of the cap 1 into which it is secured with acrylicresin. The head of the radius is excised, and

the ulnar 24 is recessed to receive the socket 6 for securement withacrylic cement.

An additional point to note is that the natural shape of the trochleaforms a neck behind the cap 1. This neck serves to facilitate flexionand extension between the bones in the natural joint and serves asimilar function in the prosthesis. The tapered shaping 8 of the endportions of the socket side walls also contributes to this function,these portions being such as to correspond approximately to those partsof the coronoid and olecranon processes which are replaced thereby. Moreparticularly, the side wall end portions replacing the part of theolecranon process closest to the articular surface can then pass intothe olecranon fossa of the humerus to allow the device to move towards aposition of full extension in the natural joint.

In the second illustrated embodiment the humeral component is again inthe form of an open-ended trough denoted at 31 of which a first portionis a duplication of FIGS. 1 and 2 with bearing surface 2, longitudinalaxis 3, and fixation surface 4. This first portion is augmented at oneend by a second portion comprising a convex, part-annular, sphericalbearing surface 32 centred on the axis 3, the spherical shaping of thissurface being of greater radius than the surface 2, but thecircumferential extent of the part-annular shaping around the axis 3 isthe same as that of the surface 2. The component is intended to beintegral in this instance and the surfaces 2 and 32 are separated by agroove to facilitate their formation. However, the component can beformed in separate first and second portions connectable in any suitablemanner to dispose the surfaces 2 and 32 in the illustrated relativepositions in predetermined manner. In either event, the fixation surface4 continues behind the surface 32.

The associated radial component of FIG. 9 is denoted at 41 and comprisesa disc member 42, having a concave part-spherical bearing surface 43 inone face thereof, while the other face thereof defines the respectivefixation surface and has a short stem 44 projecting therefrom. Thebearing surface 43 is complementary with the second portion bearingsurface 32 of the associated humeral component.

The humeral and radial components just described are intended to be usedwith an ulnar component such as that illustrated in FIGS. 3 to 5, andimplantation is basically as with the first embodiment except that thepreparation of the humerus is extended to receive the longer humeralcomponent 31, and the distal end of the radius is not excised but isprepared to receive the radial component 41. In any event, implantationis effected whereby the humeral component first and second portionbearing surfaces 2 and 22 are in respective mutual articulatoryengagement with the bearing surfaces 7 and 43 of the ulnar and radialcomponents.

The advantages of these devices according to the invention can beappreciated by comparison with the currently conventional form ofendoprosthetic elbow joint devices. As noted initially above, the latterdevices are normally of all-metal construction, mechanical hinge form,involving intramedullary stem fixation in both the humerus and ulna. Thepresent devices are of simpler and more compact geometry which fitswithin the capsule of the natural joint to be held in bearing relationthereby without the use of a mechanical hinge structure. The absence oflong intramedullary stems in the present devices contributessignificantly to their compactness and correspondingly reduces the needfor removal and excavation of bone. Further-- more, the absence of longintramedullary stems reduces the dangers associated with any infectionwhich may occur and simplifies the total removal of infected material ifthis becomes necessary. Similarly, the absence of a mechanically-linkedhinge structure simplifies the implantation procedure and, perhaps moreimportant, simplifies removal of the device in the event that thisbecomes necessary. Also, the absence of a mechanically-linked hingelimits the forces which can be transmitted through the prosthesis andthereby reduces the probability of loosening of the components.

The absence of long intramedullary stems and a mechanically linkedhinged structure is further advantageous in respect of manufacture.intramedullary stems often involve the provision of oppositely handedcomponents for left and right and joint, and linked structures commonlyinvolve the production of at least three components for each device.These requirements can be redundant with the present invention.

There is also advantage in the preferred choice and application ofmaterials to the present device. Metal/- plastics material combinationsare favored for other endoprosthetic bone joint devices for their lowfriction bearing properties, and this is taken into account in thepresent device. Moreover, the preferred allocation of materials to thecomponents allows the use of bearing surfaces of relatively large radiuswhich spreads the bearing load over a greater area and acts againstdislocation, while the metal cap component can be of thinner walled formto reduce the requirement for bone removal, and the plastics material ofthe socket component or components, which material is more susceptibleto wear, is also the thicker walledcomponent.

We claim:

1. A total endoprosthetic elbow joint device, comprising:

a humeral component in the form of a cap having a symmetricalopen-ended, entirely U-shaped channel relative to a longitudinal axistherethrough, said humeral component defining an outer bearing surfaceof circular arcuate cross section centered on said axis, and defining aninner fixation surface forming a slot encompassing said axis; and

an ulnar component in the fonn of a socket having an open-endedgenerally U-shaped channel relative to said axis, said ulnar componentdefining an inner bearing surface substantially complementary to andengaged with at least a longitudinal portion of said outer bearingsurface of said humeral component for mutual articulation about saidaxis between said bearing surfaces, and defining an outer fixationsurface, said inner bearing surface and the bordering parts of saidouter fixation surface being convergently tapered towards each of thelongitudinal ends of said ulnar component, said fixation surfaces beingadapted to be secured relative to respective bone ends by a cementitiousgap filling medium.

2. A device according to claim 1 wherein said inner fixation surface isin the form of a longitudinal slot having a cross-sectional shape withparallel sides joined by a semi-circle, which shape is symmetricallylocated relative to said outer bearing surface and being inwardlynon-diverging in cross section.

3. A device according to claim 1 wherein said tapering follows convex,circular arcuate shaping.

4. A device according to claim 1 wherein said outer fixation surface isof generally wholly tapered form converging remotely from said innerbearing surface.

5. A device according to claim 4 wherein said outer fixation surfacetapering is of generally frusto-pyramidal form.

6. A device according to claim 1 wherein said outer bearing surfacecomprises a further portion of convex, substantially part-sphericalshaping, located adjacent one end of the first-mentioned portion,centred on said axis, and having greater radius than said first portion;and said device further comprises a radial component having a bearingsurface having a concave shaping complementary to and engaged with saidconvex surface for mutual articulation therebetween; and a fixationsurface adapted for securement with the radius.

7. An endoprosthetic elbow joint device comprising:

a humeral component in the form of a cap having an open-ended, generallyU-shaped channel relative to a longitudinal axis therethrough, saidhumeral component defining and outer bearing surface with apart-circular-cylindrical first longitudinal portion and apart-spherical second longitudinal portion of greater radius than saidfirst portion, and defining an inner fixation surface forming a slotencompassing said axis;

an ulnar component in the form of a socket having an open-endedgenerally U-shaped channel shape relative to said axis, said ulnarcomponent defining a partcircular-cylindrical inner bearing surfacecomplementary to and engaged with said outer bearing surface of saidfirst portion; and

a radial component defining a bearing surface which is concave relativeto, and engaged with, said outer bearing surface of said second portion.

8. A total endoprosthetic elbow joint device comprising:

a humeral component having a first symmetrical, entirely U-shapedchannel form relative to a longitudinal axis therethrough, which formdefines a longitudinal outer surface of convex circular cylindricalshape centered on said axis, and a longitudinal inner surface ofopen-ended shape encompassing said axis, said convex cylindrical shapehaving major circular segmental extent in cross section; and

an ulnar component of generally U-shaped channel form, which formdefines a longitudinal inner surface of concave circular cylindricalshape complementary to and engaged with said convex cylindrical shape ofsaid humeral component for mutual articulation about said axis, and agenerally convex outer surface, said concave cylindrical shape havingminor circular segmental extent in cross section, and the longitudinalends of said concave cylindrical shape and adjacent parts of said convexouter surface being convergently tapered, said fixation surfaces beingadapted to be secured relative to respective bone ends by a cementitiousgap filling medium.

9. A total endoprosthetic elbow joint device, comprising:

a humeral component having a first entirely U- shaped channel formrelative to a longitudinal axis therethrough, said first form defining alongitudinal outer bearing surface and a longitudinal inner fixationsurface, said outer bearing surface having a symmetrical longitudinalshape and a convex circularly arcuate cross-sectional shape which iscentered on said axis and of greater arcuate extent than a semi-circle,said inner fixation surface having an open-ended symmetrical shape and asymmetrical concave inwardly non-diverging cross-sectional shape, andsaid outer bearing surface and said inner fixation surface beingmutually symmetrically located; and

an ulnar component of a second U-shaped channel form defining alongitudinal inner bearing surface and a longitudinal outer fixationsurface, said inner bearing surface being complementary to and engagedwith said outer bearing surface for mutual articulation about said axis,said inner bearing surface having circularly arcuate cross-sectionalshape of lesser arcuate extent than a semi-circle, and the longitudinalends of said inner bearing surface and bordering parts of said outerfixation surface being convergently tapered, said fixation surfacesbeing adapted to be secured relative to respective bone ends by acementitious gap filling medium.

1. A total endoprosthetic elbow joint device, comprising: a humeralcomponent in the form of a cap having a symmetrical open-ended, entirelyU-shaped channel relative to a longitudinal axis therethrough, saidhumeral component defining an outer bearing surface of circular arcuatecross section centered on said axis, and defining an inner fixationsurface forming a slot encompassing said axis; and an ulnar component inthe form of a socket having an open-ended generally U-shaped channelrelative to said axis, said ulnar component defining an inner bearingsurface substantially complementary to and engaged with at least alongitudinal portion of said outer bearing surface of said humeralcomponent for mutual articulation about said axis between said bearingsurfaces, and defining an outer fixation surface, said inner bearingsurface and the bordering parts of said outer fixation surface beingconvergently tapered towards each of the longitudinal ends of said ulnarcomponent, said fixation surfaces being adapted to be secured relativeto respective bone ends by a cementitious gap filling medium.
 2. Adevice according to claim 1 wherein said inner fixation surface is inthe form of a longitudinal slot having a cross-sectional shape withparallel sides joined by a semi-circle, which shape is symmetricallylocated relative to said outer bearing surface and being inwardlynon-diverging in cross section.
 3. A device according to claim 1 whereinsaid tapering follows convex, circular arcuate shaping.
 4. A deviceaccording to claim 1 wherein said outer fixation surface is of generallywholly tapered form converging remotely from said inner bearing surface.5. A device according to claim 4 wherein said outer fixation surfacetapering is of generally frusto-pyramidal form.
 6. A device according toclaim 1 wherein said outer bearing surface comprises a further portionof convex, substantially part-spherical shaping, located adjacent oneend of the first-mentioned portion, centred on said axis, and havinggreater radius than said first portion; and said device furthercomprises a radial component having a bearing surface having a concaveshaping complementary to and engaged with said convex surface for mutualarticulation therebetween; and a fixation surface adapted for securementwith the radius.
 7. An endoprosthetic elbow joiNt device comprising: ahumeral component in the form of a cap having an open-ended, generallyU-shaped channel relative to a longitudinal axis therethrough, saidhumeral component defining and outer bearing surface with apart-circular-cylindrical first longitudinal portion and apart-spherical second longitudinal portion of greater radius than saidfirst portion, and defining an inner fixation surface forming a slotencompassing said axis; an ulnar component in the form of a sockethaving an open-ended generally U-shaped channel shape relative to saidaxis, said ulnar component defining a partcircular-cylindrical innerbearing surface complementary to and engaged with said outer bearingsurface of said first portion; and a radial component defining a bearingsurface which is concave relative to, and engaged with, said outerbearing surface of said second portion.
 8. A total endoprosthetic elbowjoint device comprising: a humeral component having a first symmetrical,entirely U-shaped channel form relative to a longitudinal axistherethrough, which form defines a longitudinal outer surface of convexcircular cylindrical shape centered on said axis, and a longitudinalinner surface of open-ended shape encompassing said axis, said convexcylindrical shape having major circular segmental extent in crosssection; and an ulnar component of generally U-shaped channel form,which form defines a longitudinal inner surface of concave circularcylindrical shape complementary to and engaged with said convexcylindrical shape of said humeral component for mutual articulationabout said axis, and a generally convex outer surface, said concavecylindrical shape having minor circular segmental extent in crosssection, and the longitudinal ends of said concave cylindrical shape andadjacent parts of said convex outer surface being convergently tapered,said fixation surfaces being adapted to be secured relative torespective bone ends by a cementitious gap filling medium.
 9. A totalendoprosthetic elbow joint device, comprising: a humeral componenthaving a first entirely U-shaped channel form relative to a longitudinalaxis therethrough, said first form defining a longitudinal outer bearingsurface and a longitudinal inner fixation surface, said outer bearingsurface having a symmetrical longitudinal shape and a convex circularlyarcuate cross-sectional shape which is centered on said axis and ofgreater arcuate extent than a semi-circle, said inner fixation surfacehaving an open-ended symmetrical shape and a symmetrical concaveinwardly non-diverging cross-sectional shape, and said outer bearingsurface and said inner fixation surface being mutually symmetricallylocated; and an ulnar component of a second U-shaped channel formdefining a longitudinal inner bearing surface and a longitudinal outerfixation surface, said inner bearing surface being complementary to andengaged with said outer bearing surface for mutual articulation aboutsaid axis, said inner bearing surface having circularly arcuatecross-sectional shape of lesser arcuate extent than a semi-circle, andthe longitudinal ends of said inner bearing surface and bordering partsof said outer fixation surface being convergently tapered, said fixationsurfaces being adapted to be secured relative to respective bone ends bya cementitious gap filling medium.